The present invention relates to a catalyst material for the oxidation and/or oxidative dehydrogenation of hydrocarbons, a catalyst for the oxidation and/or oxidative dehydrogenation of hydrocarbons, a use of the catalyst material or of the catalyst, a method for producing a catalyst material for the oxidation and/or oxidative dehydrogenation of hydrocarbons and a method for the selective oxidation of propane to acrylic acid.
MoVNbTeOx mixed oxides for the oxidation of propane to acrylic acid are state of the art. More than 200 patents and numerous scientific publications discuss catalysts based on MoVNbTe mixed oxides. The promotion of these mixed oxides with other metals of the periodic table is known. The highest acrylic acid yields previously described are 50%.
The MoVNbTe base system, based on four elements, for a catalyst was first proposed by Mitsubishi for the ammoxidation of propane to acrylonitrile (1991) and the oxidation to acrylic acid (1994). Since then, numerous further publications have dealt with the improvement of this catalyst for example by promotion, supporting and “spiking” with noble metals.
The previously achieved yields of 50% are not sufficient for a commercialization of the process. Yields of approximately 60 to 65% acrylic acid are desired. However, such yields have not yet been achieved with multi-metal systems based on four or five elements.
Catalysts for the oxidation and/or oxidative dehydrogenation of alkanes are usually complex multi-metal oxides, based on molybdenum and vanadium oxides. As previously explained, catalysts for the selective oxidation of propane to acrylic acid are of particular interest, wherein only yields of approximately 50% acrylic acid have been achieved with mixed oxides of molybdenum, vanadium, niobium and tellurium.
MoVNbTeOx catalysts mainly consist of two orthorhombic phases, which are called “M1” and “M2” (T. Ushikubo, K. Oshima, A. Kayou, M. Hatano, Studies in Surface Science and Catalysis 112, (1997), 473). The phase M1 seems to play a part in the propane activation as an example of an oxidative dehydrogenation, while the phase M2 could be active and selective in the oxidation of propylene to acrylic acid. The M2 phase has more tellurium than the phase M1. It is assumed that Te is an active element in the propylene conversion. It is additionally assumed that Te has a stabilizing effect on the M1 phase.
According to P. De Santo et al., Z. Kristallogr. 219 (2004) 152, the main phases M1 and M2 in multi-metal oxide catalysts for the oxidation of propane can be described for example with the following structural formulae:Mo1V0.15Te0.12Nb0.128O3.7 or Mo7.8V1.2Te0.937Nb1O28.9  M1Mo1V0.32Te0.42Nb0.08O4.6 or Mo4.31V1.36Te1.81Nb0.33O19.81  M2
Attempts have also been made to partially replace tellurium with caesium in the M2 structure. An improved activity for the ammoxidation of propylene to acrylonitrile was observed with such a catalyst (H. Hibst, F. Rosowski, G. Cox, Catal. Today 2006, 117, 234-241).
Furthermore, as mentioned above, promotions of the MoVNbTe base system with other metals have been tested. For example, WO 2008/046843 describes mixed oxide catalysts which contain bismuth.